1. Field of the Invention
The present invention relates to an optical disc recording and playback apparatus capable of accurately detecting a specific information signal from a wobbling (meandering) shape provided in guide grooves and information pit sequences on an optical disc medium and to a signal detection method for use with the optical disc recording and playback apparatus.
2. Description of the Related Art
Hitherto, in rewritable optical discs, such as CD-Rs and DVD-RWs, guide grooves are formed in such a manner as to wobble (meander), and track address information and a reference timing signal for generating a writing clock signal are superposed by using this wobble. Furthermore, in read-only optical discs, attempts to superpose an electronic watermark, such as copyright information, by arranging information pit sequences so as to wobble, have been made.
As a method for accurately detecting an information signal (hereinafter referred to as a “wobble signal”) recorded by such a wobble, it is disclosed in U.S. Pat. No. 5,339,302 that, for example, based on output obtained by difference signal detection means formed of a two-division light-receiving element, gain control is performed so that the detection output of each of the divided light-receiving elements becomes equal. This method has the effect of preventing a phenomenon in which, when a gradient occurs between an objective lens and an optical disc or when there is an error at the position where a light-receiving element is mounted, residual components occur in the difference between detection signals of the two-divided light-receiving elements, and leakage due to recording marks occurs in the wobble detection signal after recording, causing S/N of the playback signal to deteriorate.
With similar purposes, a method of reducing influences of a recording signal by subtracting detection output in each light-receiving element of the two-division light-receiving element after the detection output is normalized by an RF signal such that the outputs of the two-division light-receiving element are added together has been proposed in, for example, U.S. Pat. No. 5,459,706.
Another method has been proposed in, for example, U.S. Pat. No. 6,487,149, in which a wobble signal is detected by using a four-division light-receiving element, which is divided in a direction tangent to the tracks and in a direction at right angles to the tangent line, and when prepits (LPP) recorded in intermediate portions (so-called land portions) of mutually adjacent grooves, and recording marks are to be played back, influences on the wobble signal are reduced.